In the semiconductor industry, substrates are quite often different; product substrates or carrier substrates are connected to one another. Bonding is cited as the connecting process. Two different types of bonds can be distinguished: the temporary bond and the permanent bond. In temporary bonding, a first substrate, in most cases a product substrate, is bonded to a second substrate, in particular a carrier substrate, in order to stabilize the product substrate by the carrier substrate.
After additional processes on the product substrate, the product substrate can be removed from the carrier substrate. In technical terminology, the removal process is called debonding.
In permanent bonding, an irreversible connection between two substrates, in most cases two product substrates, is sought. This type of bonding is used primarily in the building-up of substrate stacks with different functional planes. In the publication of Dragoi, V. and Pabo, E., Wafer Bonding Process Selection, The Electrochemical Society, ECS Transactions January 2010; 33: 509-517, for example, there is an overview on different bonding methods.
Primarily before the permanent bonding, product substrates have to be aligned to one another with a very high precision via alignment marks, which are located on their surfaces. In this case, to date, the alignment and the bonding of the substrates is done mainly in different modules: an alignment module and a bonding module. The latter is referred to in simplified terms as a bonder. A critical aspect of the separation of the alignment module and the bonding module exists in the transport of the substrates that are aligned to one another from the alignment module to the bonding module. In this way, even though it may be a very short distance, the two substrates can shift toward one another. Therefore, an attaching of substrates aligned toward one another is necessary.
In the state of the art, the attaching of two substrates is done, for example, with mechanical clamps. In most cases, the mechanical clamps are connected to a substrate holder, e.g., a chuck or fixture. One of the two substrates lies directly on the substrate holder. After the second substrate is aligned relative to the first substrate, the two substrates are brought into contact. Very often, spacers that are inserted from the edge between the two substrates are used in order to prevent the complete contact of the two substrates with one another up until the actual bonding process. Independent of the use of the spacers, mechanical clamps can attach both substrates on the substrate holder. If the substrate holder is used to retain and attach the two substrates, substrate holders and substrates have to be transferred from the alignment module to the bonding module either manually or fully automatically by a robotic arm.